Directing beams of light in specific directions has many applications, and many technologies exist that can accomplish this task. Light, also known as radiation, may be composed of a broad distribution of wavelengths (broad band), such as white light, or may be a very narrow band of wavelengths, such as produced from a typical laser (narrow band). The wavelengths that compose light may be in the visible range, detectable by our eyes, or outside the visible range. Light just beyond the visible range on the long wavelength side of the spectrum is known as infra-red radiation. Light just beyond the visible range on the short wavelength side of the spectrum is known as ultra-violet.
Beams of light may be directed by various means, but directing light by means of a reflecting, movable surface, or mirror, is the most relevant to the present invention. A technology that can provide a reflective surface, and move that reflective surface in a controlled, high speed manner can find application in uses such as microscopy, projection displays, laser sensors, and similar. Should these technologies be enabled in a manner that makes them immune from distortion or damage due to external vibrations, accelerations, and gravitational orientations, the technologies become useful in a broader range of harsh conditions.
There are a number of actuation technologies know in the prior art, when coupled to reflective mirrors provide controlled beam steering. For example, there are a variety of methods for actuation that utilize electromagnetic effects. One method of directing light in a controlled manner at high speeds uses an electromagnetic device known as a galvanometer. This technology uses permanent magnets and/or ferromagnetic materials with electrical coils. Electrical current driven through the device initiates motion that can be controlled in a closed loop or an open loop manner. This actuation technology coupled to a mirror can provide a high speed mechanism to control and direct light.
It has been observed that galvanometer-based technologies consume significant electrical power under operation, making them incompatible for applications where electrical power is constrained. The electrical power consumption is largely a function of the mass of the mirror being moved, and the fact that significant energy is expended to accelerate the mirror to a position, then decelerate the mirror to stop at the desired position. The back and forth oscillatory nature of the devices is not as energetically favorable with respect to a technology that continuously rotates. It has been further observed that the mechanical complexity of the construction of galvanometer-based technologies limits the ability to miniaturize this technology to achieve low cost.
Light can also be directed in a controlled manner using mirror systems driven by voice coil actuators/motors (VCAs). Voice coil motors are typically relatively simple electrical devices, which are similar to a galvanometer, and sometimes also called a solenoid. Electrical energy applied to the windings drives a core linearly, driven by magnetic repulsion. Voice coil motors coupled to the edges of a mirror can be actuated in a controlled manner to tile the mirror and effectively direct light.
It has been observed that voice coil mirror systems consume significant amounts of electrical power, and given that they have multiple parts including fine electrical windings, they are difficult to miniaturize at low cost. The electrical power consumption is largely a function of the mass of the mirror being moved, and the fact that significant energy is expended to accelerate the mirror to a position, then decelerate the mirror to stop at the desired position. The back and forth oscillatory nature of the devices is not as energetically favorable with respect to a technology that continuously rotates.
Another technology that uses reflective surfaces for directing light in a controlled manner is electrostatic actuation. This technology uses that fact that when voltage is applied across two surfaces at close proximity, positive and negative charges collect on the respective surface, and an attractive force is generated. This actuation effect can be applied in a beam steering technology by using the force generated, and the resulting motion of attractive surfaces to change the angle of a mirror.
It has been observed that electrostatic actuation results in small movements, which in turn, even when mechanically amplified into larger angles, results in modest angles of motion in the mirror.
Piezoelectric effects also can be coupled to a mirror for beam steering. Certain materials expand when subject to high voltages, in a process known as the piezoelectric effect. It has been observed that mirror systems driven by piezoelectric effects, similar to electrostatic actuators, deliver multiple angles of motion in the mirrors.
Electrothermal actuation can be used to drive controlled angular deflection in mirrors. This class of device takes advantage of the fact that most materials expand in length when heated. By careful design, electrical power can be dissipated selectively in electrothermal actuators to produce bending or linear extension. This motion can then be coupled with mirrors to deliver a beam steering effect.
It has been observed that electrothermal actuators are relatively slow, and do not produce high speed precision motion relative to other technologies. Additionally, they typically consume significant electrical power in order to generate the high temperatures in regions of the actuators. In order to produce high temperatures and the associated thermal expansion more efficiently, some such product package the actuators in vacuum or low thermal conductivity gasses, adding to the cost of the product.
The aforementioned actuation technologies that allow for the controlled steering of light can be realized using several different manufacturing technologies. These technologies can be manufactured by traditional means, including machining, electrical winding, and hand assembly. Additionally, these beam steering technologies can be realized using semiconductor-like fabrication technologies, known as Micro-Electro-Mechanical Systems (MEMS).
As these devices are miniaturized, typically the actuation speeds that can be realized increase, due to the reduction in the amount of mass in motion. It has been observed that traditional manufacturing methods such as used in galvanometers and voice coil technologies do not scale down to small sized cost effectively. MEMS manufacturing technology has the capability of forming high precision mechanical structures at sub-millimeter scales, but it has been observed that the beam steering devices manufactured using MEMS fabrication, even when produced on large silicon wafer, do not achieve sufficiently low cost in high production volume. This is generally due to the complexity of each manufacturing step, the number of manufacturing steps, and the complex equipment typically required.
Another technology that is effective in directing beams of light in a controlled manner is known as a polygonal scanner, in which a polygon with reflective outer surfaces is rotated. Incident light reflecting of the rotating polygon's perimeter is scanned in three-dimensional (3D) space based on the speed of the polygons, number of outer sides, and the angle of each mirror side. This approach is energetically favorable with respect to the oscillatory technologies where a mirror is accelerated and decelerated back and forth, but lacks the ability for the mirror to maintain a fixed position if required. Polygonal scanner mirrors are typically mounted on a shaft on bearings, and is rotated using an electromagnetic motor. Polygonal scanners may be configured as a rotating plane with one or two sides that are reflective, or may be a multi-sided polygon with several hundred of reflective faces on the perimeter. Typical mirrors found in these devices have three to eight sides. The mirrors rotate on bearings that may be based on ball bearings or air bearing technology. Polygonal mirrors have found broad application in markets such as bar code readers, 3-D imaging, light detection and ranging (LiDAR), laser printing, and light shows for entertainment purposes. Polygonal mirrors are typically formed in lightweight metals such as aluminum, but some applications use copper for low speed stability. For low cost application the polygonal mirrors are formed with plastics. The outer reflective surfaces are formed with the economic and optical needs of the application in mind, and typically include aluminum, gold, silver, or nickel.
It has been observed that polygonal mirror scanners that use ball bearing based bearing systems can be susceptible to dust and moisture from the environment and under continuous operation, and typically have a lifetime for reliable operation that is under two years. Ball bearing based bearing systems are more robust under mechanical forces and vibration than alternative air bearings, but also can be damaged due to external forces, gravitational changes, and vibrations. It has also been observed that polygonal mirror scanners that use air bearings have long lifetimes when used in stationary, low vibrational environments, but are highly susceptible to shock and vibration that can result in catastrophic failure. Polygonal air bearings keep the high speed rotating shaft and mirror separate from the fixed mounting and motor surfaces by creating a high speed layer of air in a designed gap. This air can be actively pumped into the bearing gap, or naturally entrained into the air bearing gap by the rotation of the device. When subjected to significant acceleration, the suspended moving mass can bridge that gap, colliding with the fixed surfaces and initiate an imbalance in the high speed rotation, leading to catastrophic failure.